Correctly identify gRPC requests in default on_response callback (#278

)

* use grpc status instead of html status in grpc-web on_response_trace

* add changelog entry for pr#278

Co-authored-by: Joe Dahlquist <joe@arcanyx.com>

tower-http/CHANGELOG.md

@@ -21,7 +21,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Fixed
 
-- None.
+- **trace:** Correctly identify gRPC requests in default `on_response` callback ([#278])
+
+[#278]: https://github.com/tower-rs/tower-http/pull/278
 
 # 0.3.4 (June 06, 2022)
 

tower-http/src/trace/on_response.rs

@@ -264,10 +264,23 @@ impl<B> OnResponse<B> for DefaultOnResponse {
 fn status<B>(res: &Response<B>) -> Option<i32> {
     use crate::classify::grpc_errors_as_failures::ParsedGrpcStatus;
 
+    // gRPC-over-HTTP2 uses the "application/grpc[+format]" content type, and gRPC-Web uses
+    // "application/grpc-web[+format]" or "application/grpc-web-text[+format]", where "format" is
+    // the message format, e.g. +proto, +json.
+    //
+    // So, valid grpc content types include (but are not limited to):
+    //  - application/grpc
+    //  - application/grpc+proto
+    //  - application/grpc-web+proto
+    //  - application/grpc-web-text+proto
+    //
+    // For simplicity, we simply check that the content type starts with "application/grpc".
     let is_grpc = res
         .headers()
         .get(http::header::CONTENT_TYPE)
-        .map_or(false, |value| value == "application/grpc");
+        .map_or(false, |value| {
+            value.as_bytes().starts_with("application/grpc".as_bytes())
+        });
 
     if is_grpc {
         match crate::classify::grpc_errors_as_failures::classify_grpc_metadata(